Gas turbine engines for aircraft typically include an accessory gearbox containing a gear train drivingly connected through a tower shaft to an engine main shaft. Conventional accessory drives always require reducing the input speed which is the rotational speed of the tower shaft, for the starter/generator drive, with subsequent speed reduction for driving the remaining accessories such as the fuel pump, hydraulic pump, oil pump, AC generator, etc. In aircraft gas turbine engines of the new generation, it is desirable to have the starter/generator run at a speed higher than the tower shaft. Therefore, an accessory drive gearbox used in such new engines is required to provide an increased output speed for the new starter/generator and a decreased output speed for the other accessories.
Accordingly, there is a need to provide an improved accessory drive gearbox to meet the requirements for both increased and decreased output speeds.